The present invention relates to a loop-back control apparatus for a loop network having duplicate optical fiber transmission lines.
A loop network needs control for restoration of communications by loo-back control of duplicate transmission lines in order to avoid the adverse effect of a cut-off of the transmission line or any other fault.
In the prior art, loop control is achieved with a loop-back control apparatus provided in each of the communications nodes constituting a loop network. The prior art loop-back apparatus, however, has the problem that, if a fault occurs in the electro-optic (E/O) converter used therein under the loop-back state, signal relay can be accomplished no longer.